To reset a Canon MP258 printer showing a P07 error: 1. Enter the printer's service mode by turning it off and holding the STOP/RESET button while pressing the power button, releasing STOP/RESET and pressing it twice; 2. Download and run the resetter software, load paper, and press buttons to clear the EEPROM and print a test; 3. Turn the printer off and then on again to complete the reset.